1. Field of the Invention
The present invention relates to an image blur correction apparatus for correcting an image blur produced by hand vibration or the like in an optical equipment such as a camera or the like.
2. Related Background Art
Conventionally, various apparatuses for correcting an image blur of a camera by using a lens which is displaced in a direction perpendicular to the photographing optical axis have been proposed, and are actually put into the market in recent years.
Japanese Patent Application Laid-Open No. 2-15773 proposed by the present applicant discloses an arrangement in which a correction lens which can be displaced in a direction perpendicular to the optical axis is supported by springs, and can be driven by an actuator. This arrangement has a position detection sensor for the correction lens, and feedback control is done to always locate the correction lens at a target position (blur suppression position) upon driving.
A recent apparatus of this type will be explained below with reference to the drawings.
FIGS. 8 to 10 show a principal part (correction lens drive mechanism) of a conventional blur correction optical system. FIG. 8 is a plane view, FIG. 9A is a sectional view taken along a line 9A--9A in FIG. 8, FIG. 9B is a sectional view taken along a line 9B--9B in FIG. 8, and FIG. 10 is a back view of FIG. 8.
In these drawings, a lens holder 101 holds a blur correction lens. Yokes 102 are fixed to the lens holder, and fix magnets 103 thereto. Coils 104 are used for displacing the lens holder 101 by the so-called moving magnet method that generates a drive force in the magnets 103 upon energizing the coils 104. Hall elements 105 detect the position of the lens holder 101 by detecting magnetic fluxes coming from the magnets 103 that are displaced together with the lens holder 101. A base plate 106 serves as a base member for a parts layout. Each of two tensile coil springs 107 has two end portions which are respectively hooked on a spring lock 106a of the base plate 106 and a spring lock 101a of the lens holder 101. These tensile coil springs 107 are hooked at two opposing positions, and are designed to have identical spring characteristics such as spring constants, lengths, and the like, so that the lens center is located nearly the center of the photographing optical axis at the position where the two springs balance each other in a free state (i.e., a state wherein no electromagnetic forces (to be described later) act). A stepping motor 108 is constructed by coils 108a, yokes 108b, and a magnet 108c, and is known to those who are skilled in the art. The stepping motor 108 has a gear portion 108d (see FIG. 10). A lock ring 109 has a gear portion 109a on its outer circumferential portion, and meshes with the gear portion 108d of the stepping motor 108 to rotate through a predetermined angle.
The lens holder 101 has projections 101b, as shown in FIG. 10, and the lock ring 109 has lock edges 109b and escape edges 109c. When the lock ring 109 is rotated counterclockwise by the stepping motor 108 through the predetermined angle, i.e., reaches a state shown in FIG. 10, the projections 101b of the lens holder 101 are guided and controlled by the lock edges 109b, and the lens center is locked at a position substantially corresponding with the center of the photographing optical axis. By contrast, when the lock ring 109 is rotated clockwise through the predetermined angle, the projections 101b of the lens holder 101 are separated from the lock edges 109b of the lock ring 109, and stop at positions opposing the escape edges 109c. As a result, the lens holder 101 is released from the control of the lock ring 109, and can move upon being driven by the moving magnet method while being elastically supported by the tensile coil springs 107.
However, in the above prior art, since the tensile coil springs 107 that elastically support the lens holder 101 are simply hooked by a normal method, a relative displacement is produced between the two ends of each spring and the members to which the spring is hooked upon displacement of the lens holder 101, thus causing sliding. The sliding occurs against the frictional force between the springs and members. The correction lens suffers the following adverse influences resulting from the relative displacement and the frictional force produced upon sliding.
1) The lens holder 101 has poor stop position precision and stop position reproducibility in the free state. However, the above prior art poses no problem in the free state, since the central position is determined using the stepping motor 108 and feedback control is made using a position detection means upon blur correction driving.
2) The drive precision of the correction lens deteriorates. Especially, phase delay increases, and the response characteristics to small vibrations are impaired.